Purpose :
We are developing a second-generation large angle retinal prosthesis by Suprachoroidal-Transretinal Stimulation (STS). To obtain a good performance of mobility, it is necessary to optimize the position of electrode array. In this study, we developed a simulator of retinal prosthesis and investigated the relationship between the results of mobility test and the size or position of artificial visual field.

Methods :
Twelve healthy subjects (male: 8, female: 4, age: 21～40) wore a retinal prosthesis simulator (NIDEK). Images captured by a web-camera attached on a head-mount display (HMD) was processed by a computer and displayed on the HMD. Three types of artificial visual fields which imitate phosphenes obtained by single (5×5 electrodes, visual angle; 15°) or dual (5×5 electrodes×2, visual angle; 30°) electrode array were created. Type 1 creates lower visual field corresponding to dual array implanted upward, Type 2 creates lower visual field corresponding with single array implanted downward, Type 3 creates upper visual field corresponding with dual array implanted downward. In each type of artificial visual fields, a natural circular visual field (visual angle; 5°) co-existed at the center. Subjects were asked to walk to and avoid white circles (obstacles) attached on a black carpet (6 m long × 2.2 m wide). The circles were 10 cm in radius and 40 cm in intervals. We measured head scanning, the time to reach the endpoint, and the number of footsteps stepping into the white circles. We compared the results among 3 types of artificial visual fields.

Results :
The number of footsteps stepping into the white circles was lowest in Type 3 visual field (Bonferroni/Dunn; P=0.028, paired-t; type1 vs type3 P=0.039, type2 vs type3 P=0.012 ) . Among the different visual fields, there was no significant difference in the time to reach the end and the amount of head scanning.

Conclusions :
Dual electrode array, which creates a large upward visual field, may result in better waking performance than single electrode array with a small upward visual field or dual electrode array with a large downward visual field.

This is an abstract that was submitted for the 2017 ARVO Annual Meeting, held in Baltimore, MD, May 7-11, 2017.